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Income Taxes - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Income Tax Disclosure [Abstract]    
Net deferred income tax assets   $ 50.5
Decrease in effective tax rate 9.30%  
U.S. corporate tax rate 21.00% 35.00%
Decrease in unrecognized tax positions $ 1.9  
Interest and penalties $ 1.7